1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device which is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the present invention relates to a piezoelectric/electrostrictive device which is excellent in strength, shock resistance, and moisture resistance and which makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Description of the Related Art
Recently, it is desirable to realize a displacement element that makes it possible to adjust an optical path length and position in an order of submicron, for example, in the fields of optics, magnetic recording, and precision machining. The development for such a displacement element is advanced and is based on the use of the displacement brought about by an inverse piezoelectric effect or an electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 44, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section 204, a movable section 206, and a beam section 208 for supporting the fixation and movable sections. The displacement element is formed in an integrated manner with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 makes expansion and contraction in a direction along a line obtained by connecting the fixation section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform a circular arc-shaped displacement or a rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The actuator is driven due to the selection of the divided electrodes, and thus, a highly accurate positioning is performed at a high speed. This patent document (especially in FIG. 4) discloses a structure in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section is small, because the displacement in the direction of expansion and contraction of the piezoelectric/electrostrictive material (i.e., in the inplane direction of the plate-shaped member) is transmitted to the movable section as it is.
All of the parts of the piezoelectric actuator are made of a piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that a filler material having flexibility is supplied to a hole included in the device. However, it is clear that a decreased amount of displacement resulting from the inverse piezoelectric effect or the electrostrictive effect remains in effect, even when the filler material is supplied to the above-mentioned hole.
On the other hand, FIG. 4 in Japanese Laid-Open Patent Publication No. 63-64640 resides in the junction of a mediating member and a bimorph in which the mediating member is joined with the portion at which no divided electrode exists. The effect of the divided electrode cannot be utilized at the joined portion. That is, the junction is merely made at the bimorph portion which is not the displacement-generating section. A similar form is adopted for the junction of the head and the bimorph.
As a result, the following structure is brought about. That is, a bending displacement of the bimorph is expressed toward an internal space between the mediating member and the head. Therefore, it is impossible to effectively displace the head itself with respect to the external space.
In many cases, the conventional devices of this type have such a structure rendering it difficult to realize a high resonance frequency required for a high speed operation, or such devices have such a structure rendering it impossible to increase the displacement of the movable section. Consequently, the following contradicting structure is obtained. That is, whenever a high resonance frequency is desired, the displacement amount of the movable section is sacrificed. On the other hand, whenever the displacement amount of the movable section is increased, it is impossible to achieve the realization of a high resonance frequency.
The present invention has been made taking the foregoing problems into consideration. An object of the present invention is to provide a piezoelectric/electrostrictive device and a method for producing the same which make it possible to obtain a displacement element that is scarcely affected by harmful vibrations during its operation. Another object is to provide a device capable of achieving a high speed response with a high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance. A further object is to provide a device wherein a movable section can be greatly displaced with a high speed of the displacement action and thus, realizing a high resonance frequency. Yet another object is to provide a sensor element which makes it possible to accurately detect a vibration of the movable section.
According to the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section. One or more piezoelectric/electrostrictive elements is arranged on at least one of the thin plate sections. A hole is formed by the inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section. The movable section has a cutout portion. It is also preferable that the cutout portion includes a hollow section and/or a through-hole provided for the movable section.
Accordingly, the movable section is allowed to have a light weight owing to the presence of the cutout. Therefore, it is possible to increase the resonance frequency without decreasing the displacement amount of the movable section. Further, it is possible to appropriately decrease the rigidity of the movable section. Therefore, an advantage is obtained such that the displacement amount of the movable section can be increased. When the thin plate section, the movable section, and the fixation section are integrated into one unit, it is unnecessary to construct all parts with the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, an advantage is obtained such that the mechanical strength is high while being excellent in handling performance, shock resistance, and moisture resistance, and the operation is scarcely affected by harmful vibration (for example, residual vibration and noise vibration during high speed operation).
According to another aspect of the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; wherein a part of the inner wall of the movable section is expanded in the hole.
Accordingly, for example, when a part is attached to the movable section, it is possible to increase the a real size of a part attachment surface of the movable section, without changing the maximum length of the piezoelectric/electrostrictive device. Thus, it is possible to improve the reliability concerning the attachment of the part.
Further, the weight is increased, because the expanded section is provided. However, the expanded section is expanded toward the hole. Therefore, the center of gravity of the movable section can be located at a position deviated toward the fixation section. Any influence is hardly exerted by the decrease in resonance frequency caused by the increase in weight. In this arrangement, the part is also attached at a position deviated toward the fixation section. Therefore, the resonance frequency is scarcely decreased after the part is attached. The displacement of the movable section is not decreased as well. That is, the device is designed such that the resonance frequency is substantially improved.
In other words, according to the present invention, the degree of the influence on the resonance frequency (decrease in resonance frequency), which would be otherwise enhanced when much weight is given to the attachment of the part, can be decreased, while enlarging the areal size of the part attachment surface of the movable section, and improving the reliability concerning the attachment of the part.
In the present invention, it is also preferable that a cutout is provided for the movable section. Accordingly, it is possible to simultaneously realize a light weight of the movable section and an increase in the displacement amount of the movable section. Thus, it is possible to simultaneously achieve the mutually contradicting xe2x80x9crealization of the high resonance frequencyxe2x80x9d and the xe2x80x9cincrease in displacementxe2x80x9d.
In the invention described above, it is also preferable that the movable section is constructed to have a main movable section body and a portion which is provided for at least one surface of the main movable section body and which has an areal size larger than that of the main movable section body. When the portion, which has the areal size larger than that of the main movable section body, is utilized to attach the part, then it is possible to contemplate the reliability of the part attachment, and it is possible to enhance the reliability concerning the operation.
In the invention described above, the movable section, the fixation section, and the thin plate sections may be made of ceramics or metal. Alternatively, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Further, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
It is also preferable that the thin plate sections, the movable section, and the fixation section are composed of a ceramic substrate obtained by being integrated into one unit by simultaneously sintering a ceramic green laminate and cutting off unnecessary portions. It is also preferable that the piezoelectric/electrostrictive element has a film-shaped configuration, and it is integrated with the ceramic substrate by means of sintering.
In this arrangement, the piezoelectric/electrostrictive element may be constructed to have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive layer. Further, the piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes may be formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted to the movable section or the fixation section via the thin plate section. Accordingly, it is possible to improve the response performance. Especially, it is preferable that the piezoelectric/electrostrictive element is constructed in a stacked form comprising a plurality of the piezoelectric/electrostrictive layers and the electrodes.
When the arrangement as described above is adopted, the following features are obtained. That is, the force generated by the piezoelectric/electrostrictive element is increased. Accordingly, it is possible to obtain the large displacement. Further, owing to the increase in rigidity of the device itself, it is possible to realize the high resonance frequency, and it is easy to achieve the realization of the high speed of the displacement operation.
In the invention described above, it is also preferable that the hole is filled with a gel material. In this arrangement, although the displacement action of the movable section is restricted due to the presence of the filler material in ordinary cases, the invention described above intends to reduce the weight as a result of the formation of the cutout for the movable section, and increase the displacement amount of the movable section. Therefore, the restriction of the displacement action of the movable section by the filler material is counteracted, and it is possible to realize the effect owing to the presence of the filler material, i.e., the realization of the high resonance frequency and the maintenance of the rigidity.
According to still another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate. sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; the method comprising a step of forming the movable section having a cutout by cutting off a predetermined part after producing at least the piezoelectric/electrostrictive element on the thin plate section.
In still another aspect, the present invention preferably lies in a method comprising a step of producing a ceramic laminate by integrally sintering a ceramic green laminate including at least a ceramic green sheet having a window for forming at least the hole thereafter and ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; a step of forming the piezoelectric/electrostrictive element on an outer surface of a portion of the ceramic laminate to be formed into the thin plate section; and a cutoff step of forming the movable section having at least a cutout by means of at least one time of cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
Accordingly, the movable section is allowed to have a light weight owing to the presence of the cutout. It is possible to efficiently and easily produce the piezoelectric/electrostrictive device which makes it possible to increase the resonance frequency without decreasing the displacement amount of the movable section. It is possible to realize mass production of the high performance piezoelectric/electrostrictive device.
The phrase xe2x80x9cafter producing the piezoelectric/electrostrictive elementxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after performing the cutoff to form the movable section having the cutout.
It is also preferable that in the step of producing the ceramic laminate, the ceramic laminate is produced by integrally sintering a ceramic green laminate including a ceramic green sheet having a window for forming the movable section having at least the cutout, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; and in the cutoff step, the movable section having at least the cutout is formed by means of the cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
It is also preferable that the cutout includes a hollow section and/or a through-hole provided for the movable section.
According to still another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by the inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; the method comprising a step of forming the movable section having an expanded section expanded in the hole by cutting off a predetermined part after producing at least the piezoelectric/electrostrictive element on the thin plate section.
In still another aspect, the present invention preferably lies in a method comprising a step of producing a ceramic laminate by integrally sintering a ceramic green laminate including at least a ceramic green sheet having a window for forming at least the hole thereafter and ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; a step of forming the piezoelectric/electrostrictive element on an outer surface of a portion of the ceramic laminate to be formed into the thin plate section; and a cutoff step of forming the movable section having at least an expanded section expanded in the hole by means of at least one time of cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
Accordingly, it is possible to efficiently and easily produce the piezoelectric/electrostrictive device which makes it possible to decrease the degree of the influence on the resonance frequency (decrease in resonance frequency), while increasing the areal size of the part attachment surface of the movable section.
It is also preferable that in the step of producing the ceramic laminate, the ceramic laminate is produced by integrally sintering a ceramic green laminate including a ceramic green sheet having a window for forming the movable section formed with at least an expanded section, and the ceramic green sheets to be formed into the thin plate sections thereafter to produce the ceramic laminate; and in the cutoff step, the movable section having at least an expanded section is formed by means of the cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element.
It is also preferable for the production methods described above that in the cutoff step, the hole is simultaneously exposed by means of the cutoff treatment for the ceramic laminate. In this process, the formation of the movable section having the cutout may be performed simultaneously with the formation of the hole. There is no limitation for the sequence to perform the formation steps.
Therefore, the piezoelectric/electrostrictive device according to the present invention can be utilized as the active device including, for example, various transducers, various actuators, frequency region functional parts (filters), transformers, vibrators, resonators, oscillators, and discriminators for communication and power generation applications, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device according to the present invention can be preferably utilized for various actuators to be used for a mechanism for adjusting the displacement and the positioning and for adjusting the angle for various precision parts such as those of optical instruments and precision mechanical equipments.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.